Corrected range mismatch (DSCP values vs. raw values in the TOS byte)

Existing code assumes that DSCP values are always already shifted two bits to left - with a tiny, yet potentially fatal exception in three lines.

http://forum.pfsense.org/index.php/topic,63580.0.html

This is one of three kernel patches for 8.3, 9.0 and 10.0. While these kernel patches are already sufficient to prevent  errors triggered by selecting valid values via the GUI, separate patches will follow to clean up meaningless entries in the GUI as well.